/Engine/Plugins/Enterprise/VariantManager/Source/VariantManager/Public/VariantManager.h
Expects one for each variant. Accepts nullptr (will clear any previous thumbnail when setting)
void SetVariantThumbnails ( const [TArray](API\Runtime\Core\Containers\TArray)< [FObjectThumbnail](API\Runtime\Core\Misc\FObjectThumbnail) * > Thumbnails, const [TArray](API\Runtime\Core\Containers\TArray)< [UVariant](API\Plugins\VariantManagerContent\UVariant) * > Variants )